Move Common Context after CSE

We had something like
	 let $j = ...
	 in case foo of ... -> case $j a b c of ... -> case foo of
and moving the inner "case foo" into $j prevented CSE from happening
here.
(Although presumably the "let $j" could be moved inside the outer case
before CSE, to give CSE a greater scope here.)

compiler/simplCore/CommonContext.lhs

@@ -52,6 +52,8 @@ findInterestingLet (Let (Rec pairs) body) =
 process :: Var -> CoreExpr -> CoreExpr -> (Var, CoreExpr, CoreExpr)
 process v e body
   | idArity v <= 0 = (v, e, body)
+  -- TODO: check for non value args here. For now, ignore this let then
+  -- Possibly later: Check if all uses have the same type argument
   | otherwise
   = case contextOf v body of
         OneUse cts | not (null cts) ->

compiler/simplCore/SimplCore.lhs

@@ -190,8 +190,6 @@ getCoreToDo dflags
     demand_analyser = (CoreDoPasses ([
                            CoreDoStrictness,
                            CoreDoWorkerWrapper,
-                           simpl_phase 0 ["post-worker-wrapper"] max_iter,
-                           CoreCommonContext,
                            simpl_phase 0 ["post-worker-wrapper"] max_iter
                            ]))
 
@@ -293,6 +291,9 @@ getCoreToDo dflags
                         -- reduce the possiblility of shadowing
                         -- Reason: see Note [Shadowing] in SpecConstr.lhs
 
+        CoreCommonContext,
+        simpl_phase 0 ["post-common-context"] max_iter,
+
         runWhen spec_constr CoreDoSpecConstr,
 
         maybe_rule_check (Phase 0),